Prime Minister Tony Abbott says there is "increasing hope" that the southern Indian Ocean search for Malaysia Airlines flight MH370 will prove fruitful, after Chinese satellites detected a large object that could be debris.

Authorities have begun a fourth day of sorties into the search zone about 2,500 kilometres south-west of Perth, where they are now also searching for an object that China identified yesterday as being 22 metres long and 13 metres wide.

The object was spotted about 120 kilometres south-west of two possible objects seen on satellite images taken on March 16 and announced by the Australian Government on Thursday.

The Chinese satellite images were taken five days ago, on March 18, by the high-definition Earth observation satellite Gaofen-1.

Dimensions of the Boeing 777-200ER

Wing span: 60.9 metres

Overall length: 63.7 metres

Tail height: 18.5 metres

Fuselage diameter: 6.19 metres

The development came after a civilian plane yesterday reported sighting a number of small objects close together in the search zone, which the Australian Maritime Search Authority (AMSA) is still trying to locate.

A P3 Orion aircraft flew over the area but could see nothing but seaweed.

The Orion dropped a marker buoy to track movement of the material and a merchant ship has been sent to locate and identify it.

Speaking from Papua New Guinea this morning, Mr Abbott said one of the objects is reported to have been a wooden pallet.

He said there have been "significant developments" over the past 24 hours.

"New Chinese satellite imagery does seem to suggest at least one large object down there, consistent with the object that earlier satellite imagery discovered which I told the Australian Parliament about last week," he said.

"Yesterday one of our civilian search aircraft got visuals on a number of objects in a fairly small area in the overall Australian search zone.

"Obviously we have now had a number of very credible leads and there is increasing hope, no more than hope, that we might be on the road to discovering what did happen."

Mr Abbott said two Chinese aircraft and two Japanese Orions will today join the fleet flying into the search zone, which was yesterday expanded to 36,000 square kilometres.

"The more aircraft we have, the more ships we have, the more confident we are of recovering whatever material is down there," he said.

AMSA said it had taken into account the new object captured by Chinese satellites for its searches throughout the day.

"Very importantly, it's been detected by two different satellites 38 hours apart," he said.

"That gives us very simply an average drift speed of 1.7 knots. Now we try to apply that forward, thinking where that wreckage is going to be five days from that last image... to put search teams in that patch of water.

"I'm feeling far more optimistic today than I was yesterday."

Tracking flight MH370

The new potential sighting by Chinese satellites was dramatically announced by Malaysia's acting transport minister after he was handed a note with details during a news conference in Kuala Lumpur last night, scooping the official announcement from China.

"Whether the unusual floating object is related to the missing passenger plane awaits further analysis and verification," he said.

"Chinese sea and air rescue forces are rushing to the relevant area of the southern Indian Ocean to carry out search and rescue operations."

It came after Nationals leader Warren Truss, who was Acting Prime Minister in Mr Abbott's absence, said the search would continue until it would be "futile" to continue, and that the cost of the search was not a factor.